Mediofrontal theta-band oscillations reflect top-down influence in the ventriloquist illusion.

In the ventriloquist illusion, spatially disparate visual signals can influence the perceived location of simultaneous sounds. Previous studies have shown asymmetrical responses in auditory cortical regions following perceived peripheral sound shifts. Moreover, higher-order cortical areas perform inferences on the sources of disparate audiovisual signals. Recent studies have also highlighted top-down influence in the ventriloquist illusion and postulated a governing function of neural oscillations for crossmodal processing. In this EEG study, we analyzed source-reconstructed neural oscillations to address the question of whether perceived sound shifts affect the laterality of auditory responses. Moreover, we investigated the modulation of neural oscillations related to the occurrence of the illusion more generally. With respect to the first question, we did not find evidence for significant changes in the laterality of auditory responses due to perceived sound shifts. However, we found a sustained reduction of mediofrontal theta-band power starting prior to stimulus onset when participants perceived the illusion compared to when they did not perceive the illusion. We suggest that this effect reflects a state of diminished cognitive control, leading to reliance on more readily discriminable visual information and increased crossmodal influence. We conclude that mediofrontal theta-band oscillations serve as a neural mechanism underlying top-down modulation of crossmodal processing in the ventriloquist illusion.

Low-frequency oscillations reflect aberrant tone restoration during the auditory continuity illusion in schizophrenia.

Patients with schizophrenia (ScZ) often show impairments in auditory information processing. These impairments have been related to clinical symptoms, such as auditory hallucinations. Some researchers have hypothesized that aberrant low-frequency oscillations contribute to auditory information processing deficits in ScZ. A paradigm for which modulations in low-frequency oscillations are consistently found in healthy individuals is the auditory continuity illusion (ACI), in which restoration processes lead to a perceptual grouping of tone fragments and a mask, so that a physically interrupted sound is perceived as continuous. We used the ACI paradigm to test the hypothesis that low-frequency oscillations play a role in aberrant auditory information processing in patients with ScZ (N = 23). Compared with healthy control participants we found that patients with ScZ show elevated continuity illusions of interrupted, partially-masked tones. Electroencephalography data demonstrate that this elevated continuity perception is reflected by diminished 3 Hz power. This suggests that reduced low-frequency oscillations relate to elevated restoration processes in ScZ. Our findings support the hypothesis that aberrant low-frequency oscillations contribute to altered perception-related auditory information processing in ScZ.

Reduced low-frequency power and phase locking reflect restoration in the auditory continuity illusion.

Interruptions in auditory input can be perceptually restored if they coincide with a masking sound, resulting in a continuity illusion. Previous studies have shown that this continuity illusion is associated with reduced low-frequency neural oscillations in the auditory cortex. However, the precise contribution of oscillatory amplitude changes and phase alignment to auditory restoration remains unclear. Using electroencephalography, we investigated induced power changes and phase locking in response to 3 Hz amplitude-modulated tones during the interval of an interrupting noise. We experimentally manipulated both the physical continuity of the tone (continuous vs. interrupted) and the masking potential of the noise (notched vs. full). We observed an attenuation of 3 Hz power during continuity illusions in comparison with both continuous tones and veridically perceived interrupted tones. This illusion-related suppression of low-frequency oscillations likely reflects a blurring of auditory object boundaries that supports continuity perception. We further observed increased 3 Hz phase locking during fully masked continuous tones compared with the other conditions. This low-frequency phase alignment may reflect the neural registration of the interrupting noise as a newly appearing object, whereas during continuity illusions, a spectral portion of this noise is delegated to filling the interruption. Taken together, our findings suggest that the suppression of slow cortical oscillations in both the power and phase domains supports perceptual restoration of interruptions in auditory input.